Technical Field
The present invention relates to a process for preparing activated carbon. More specifically, the present invention relates to a process for preparing modified, mesoporous activated carbon by physicochemical treatment of waste oil fly ash. The prepared activated carbon material is suitable for hydrogen sulfide gas removal applications.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Hydrogen sulfide (H2S) is a major pollutant where the presence thereof in natural gas results in major corrosion and environmental problems. Hydrogen sulfide is toxic and is a most harmful toxin gas for human and animals. It becomes fatal when its concentration exceeds 500 ppm [Y. Elsayed, M. Seredych, A. Dallas, T. J. Bandosz, Desulfurization of air at high and low H2S concentrations, Chem. Eng. J. 155 (2009) 594-602; P. Forzatti, L. Lietti, Catalyst deactivation, 52 (1999) 165-181; W. J. Powers-Schilling, Olfaction: Chemical and psychological consideration, in: Nuisance Concern Animal. Management: Odor and Flies, Gainesville, Fla., 1995; Y. Xiao, S. Wang, D. Wu, Q. Yuan, Catalytic oxidation of hydrogen sulfide over unmodified and impregnated activated carbon, Sep. Purif. Technol. 59 (2008) 326-332—each incorporated herein by reference in its entirety]. On the other hand, the presence of H2S at concentrations higher than 5.5 mg/m3 in natural gas leads to sulfur stress cracking that reduces life of processing and handling equipment. To overcome these adverse effects, several commercial technologies have been used for H2S removal from natural gas. The amine sweetening process is widely used in industries to lower the concentration of H2S to the target level imposed by customers and downstream processors [R. Álvarez-Cruz, B. E. Sánchez-Flores, J. Torres-González, R. Antaño-López, F. Castañeda, Insights in the development of a new method to treat H2S and CO2 from sour gas by alkali, Fuel. 100 (2012) 173-176; M. Tagliabue, C. Rizzo, N. B. Onorati, E. F. Gambarotta, A. Carati, F. Bazzano, Regenerability of zeolites as adsorbents for natural gas sweetening: A case-study, Fuel. 93 (2012) 238-244—each incorporated herein by reference in its entirety]. This method is costly in term of heat required for regeneration and also produces unwanted by-products. Other treatment processes, such as membrane separation and biological treatment, either suffer from low selectivity or they are not feasible at the larger scales [ J. I. Huertas, N. Giraldo, S. Izquierdo, Removal of H2S and CO2 from Biogas by Amine Absorption, in: D. J. Markoa (Ed.), Mass Transfer in Chemical Engineering Process, In Tech Europ, 2011, pp. 132-150—incorporated herein by reference in its entirety].
Adsorption, on the other hand, can be used to capture H2S at trace levels with relatively low cost of adsorbent. This process becomes especially attractive option when an adsorbent material, such as waste oil fly ash, is available in large quantities and for low cost. Waste oil fly ash is byproduct of many industrial and power generation plant operations [M. Sharma, C. Guria, A. Sarkar, A. K. Pathak, Recycle of waste fly ash: A rheological Investigation, Int. J. Sci. Environ. Technol. 1 (2012) 285-301—incorporated herein by reference in its entirety]. Waste oil fly ash usually causes environmental pollution problems and requires safe disposal. Therefore, utilization of waste oil fly ash in removing H2S is expected to solve more than one environmental problem.
Since waste oil fly ash is pozzolanic in nature, it contains mainly unburned carbon (˜80%) with some inorganic oxides like SiO2, Fe2O3, Al2O3, and CaO and traces of heavy metals [R. Shawabkeh, M. J. Khan, A. a. Al-Juhani, H. I. Al-Abdul Wahhab, I. a. Hussein, Enhancement of surface properties of oil fly ash by chemical treatment, Appl. Surf. Sci. 258 (2011) 1643-1650—incorporated herein by reference in its entirety]. According to a survey conducted by American Coal Ash Association (ACAA) over 100 million tons of coal combustion products were produced in 2012, where only 38% of total coal combustion products were used beneficially [American Coal Ash Association, Coal Combustion Product (CCP) Production & Use Survey Report, 2012—incorporated herein by reference in its entirety]. However, utilization rate of fly ash has increased greatly in China reaching up to 67% in 2010 compared to 20% rate in 1999 [Z. Tang, S. Ma, J. Ding, Y. Wang, S. Zheng, Current status and prospect of fly ash Utilization in China, in: 2013 World Coal Ash Conference, 2013, pp. 22-27—incorporated herein by reference in its entirety]. The majority of fly ash is used in blended cements, filler for metal matrix composites, as raw material for metal recovery and as filler for polymers [R. A. Shawabkeh, Adsorption of chromium ions from aqueous solution by using activated carbo-aluminosilicate material from oil shale., J. Colloid Interface Sci. 299 (2006) 530-6; T. P. D. Rajan, R. M. Pillai, B. C. Pai, K. G. Satyanarayana, P. K. Rohatgi, Fabrication and characterisation of Al-7Si-0.35Mg/fly ash metal matrix composites processed by different stir casting routes, Compos. Sci. Technol. 67 (2007) 3369-3377; R. Navarro, J. Guzman, I. Saucedo, J. Revilla, E. Guibal, Vanadium recovery from oil fly ash by leaching, precipitation and solvent extraction processes., Waste Manag. 27 (2007) 425-38; Q. Zeng, K. Li, T. Fen-Chong, P. Dangla, Surface fractal analysis of pore structure of high-volume fly-ash cement pastes, Appl. Surf. Sci. 257 (2010) 762-768; M. a. Al-Ghouti, Y. S. Al-Degs, A. Ghrair, H. Khoury, M. Ziedan, Extraction and separation of vanadium and nickel from fly ash produced in heavy fuel power plants, Chem. Eng. J. 173 (2011) 191-197; K. T. Hideaki Tokuyama, Susumu Nii, Fumio Kawaizumi, Characterization of Al-Cu alloy reinforced fly ash metal matrix composites by squeeze casting method, Int. J. Engg. Sci. Technol.5 (2013) 71-79; A. K. Senapati, A. Bhatta, S. Mohanty, P. C. Mishra, B. C. Routra, An extensive literature review on the usage of fly ash as a reinforcing agent for different matrices, Int. J. Innov. Sci. Mod. Eng., vol. 2, no. 3(2014) 4-9—each incorporated herein by reference in its entirety]. Recently, oil fly ash has gained particular attention as potential adsorbent for several adsorbate due to its high carbonaceous content and low cost [A. L. Yaumi, R. Aww. K. ShaWabkeh, ilbnesllvaleed A. Hussem, United States Patent, U.S. Pat. No. 8,545,781 B1, 2013; A. L. Yaumi, I. a. Hussien, R. a. Shawabkeh, Surface modification of oil fly ash and its application in selective capturing of carbon dioxide, Appl. Surf. Sci. 266 (2013) 118-125; B. Rubio, M. T. Izquierdo, Coal fly ash based carbons for SO2 removal from flue gases., Waste Manag. 30 (2010) 1341-7; CN103626174A; US20140197020A1; KR996431B1—each incorporated herein by reference in its entirety]. Izquierdo et al studied SO2 removal using activated carbon (AC) produced from oil agglomerated coal fly ash. They compare the adsorption efficiency of anthracite coal based fly ash activated carbon with bituminous-lignite blended coal fly ash activated carbon and concluded that the latter is superior with 28 mg/g uptake capacity [B. Rubio, M. T. Izquierdo, Coal fly ash based carbons for SO2 removal from flue gases., Waste Manag. 30 (2010) 1341-7—incorporated herein by reference in its entirety]. With some chemical treatment, the porosimetric characteristics of ash may be enhanced to obtain a high surface area AC. Thus obtained, AC can be used to remove pollutants from flue gas. Yaumi et al. used treated oil fly ash for the adsorption of CO2 under different flow conditions. A removal capacity of 240 mg CO2/g-treated OFA was achieved. The interactions between CO2 and ash surface were reported to be endothermic in nature [A. L. Yaumi, R. Aww. K. ShaWabkeh, ilbnesllvaleed A. Hussem, United States Patent, U.S. Pat. No. 8,545,781 B1, 2013; A. L. Yaumi, I. a. Hussien, R. a. Shawabkeh, Surface modification of oil fly ash and its application in selective capturing of carbon dioxide, Appl. Surf. Sci. 266 (2013) 118-125—each incorporated herein by reference in its entirety].
Various treatment strategies could be implemented to increase the porosity and create some ordering of structure like in the synthesis of zeolites [A. Alastuey, E. Herna, X. Querol, N. Moreno, J. C. Uman, F. Plana, Synthesis of zeolites from coal fly ash: an overview, Int. J. Coal Geol 0.50 (2002) 413-423; M. Wdowin, M. Franus, R. Panek, L. Badura, W. Franus, The conversion technology of fly ash into zeolites, Clean Technol. Environ. Policy. (2014). M. Visa, A. Duta, TiO2/fly ash novel substrate for simultaneous removal of heavy metals and surfactants, Chem. Eng. J. 223 (2013) 860-868; M. M. Maroto-valer, Z. Lu, Y. Zhang, Z. Tang, Sorbents for CO2 capture from high carbon fly ashes, Waste Manag. 28 (2008) 2320-2328—each incorporated herein by reference in its entirety]. For example, external heating of fly ash with acid mixture involves various sulfonation and nitrification reactions including the formation of phosphate functional groups. As a result oxides of sulfur and nitrogen and carbon dioxide are released during the chemical activation process [B. Bournonville, A. Nzihou, P. Sharrock, G. Depelsenaire, Stabilisation of heavy metal containing dusts by reaction with phosphoric acid: study of the reactivity of fly ash., J. Hazard. Mater. 116 (2004) 65-74; R. A. Shawabkeh, Synthesis and characterization of activated carbo-aluminosilicate material from oil shale, Microporous Mesoporous Mater. 75 (2004) 107-114—each incorporated herein by reference in its entirety]. Treatment of fly ash with acids also introduces hydrophilic groups like carboxylic and hydroxyl groups on the surface of ash [E. D. Dimotakis, M. P. Cal, J. Economy, M. J. Rood, S. M. Larson, Chemically treated activated carbon cloths for removal of volatile organic carbons from gas streams: evidence for enhanced physical adsorption., Environ. Sci. Technol. 29 (1995) 1876-80—incorporated herein by reference in its entirety].
Several kinds of carbon based adsorbents have been employed to capture H2S from gas stream. These adsorbents include agro-based activated carbon, coal based and impregnated activated carbon [J. Kazmierczak, P. Nowicki, R. Pietrzak, Sorption properties of activated carbons obtained from corn cobs by chemical and physical activation, Adsorption. 19(2013) 273-281; H. S. Choo, L. C. Lau, A. R. Mohamed, K. T. Lee, Hydrogen sulfide adsorption by alkaline impregnated coconut shell activated carbon, J. Eng. Sci. Technol. 8 (2013) 741-753; D. Choi, J. Lee, S. Jang, B. Aim, D. Choi, Adsorption dynamics of hydrogen sulfide in impregnated activated carbon bed, Adsorption. 14 (2008) 533-538; A. Bagreev, J. Angel Menendez, I. Dukhno, Y. Tarasenko, T. J. Bandosz, Bituminous coal-based activated carbons modified with nitrogen as adsorbents of hydrogen sulfide, Carbon. 42 (2004) 469-476—incorporated herein by reference in its entirety].
In view of the foregoing, there remain numerous, ongoing efforts directed towards development of processes for preparing activated carbon with new raw materials. The present disclosure provides a process for manufacturing modified, mesoporous activated carbon where the carbon activation procedure is relatively simple and straightforward, and the surface area of the activated carbon can be dramatically increased during the manufacturing process.